The present invention relates to the field of converting optical images to electrical pulse trains.
It is deemed desirable to fabricate very long high density linear arrays of PbS and PbSe infrared sensitive photoconductor material for scanning optical images and converting them into electrical signals representative of the images. The prior art suggests the use of arrays of PbS and arrays of PbSe for detecting infrared radiation. See SPIE, Volume 197, pp. 9-18 (1979).
While U.S. Pat. No. 3,808,435 teaches the use of arrays of photosensitive material detecting infrared radiation, this material is electically coupled to a CCD semi-conductor chip through numerous separate electrical leads. See FIG. 3 and column 2, lines 1 through 10. The CCD devices are employed to serially generate electrical signals proportional to the intensity of infrared radiation projected upon the light sensitive elements connected in parallel to the CCD stages. The image to be converted into electrical pulse trains is scanned across the array of detectors so that portions of the image are progressively sensed by successive detectors in respective columns of the array. The result is the shifting, along the length of the CCD, of injected charges in synchronism with the scanning of the image. In U.S. Pat. No. 3,883,437, each IR detector is coupled to a particular CCD stage via electrical leads which pass through a set of openings in the insulating oxide layer. See the bottom of column 2 and column 5 lines 53 through 55. In U.S. Pat. No. 4,064,533, PbS elements are electrically connected to a silicon CCD device via conductors 24 shown in FIG. 1; see the top of column 6.
Thus the prior art teaches the use of discrete elements of IR sensitive material electrically coupled via leads or other metallic electrodes to multiplexing circuitry in a silicon wafer, such as a CCD. The necessity of providing a separate lead or contact from each detector, to run off of the focal plane where the IR detectors are positioned, to an associated stage of a multiplexing unit, for converting the parallel signals into a serial pulse train, makes it impractical to fabricate arrays greater than 50 to 100 elements long, due to the bonding of numerous leads between the photosensors and the multiplexer units.